I know FM has a better sound with less static but, the Ancient Modulation stations are not going away as fast as a lot of people think in markets #1 & 3. Disney / ESPN did not get the big rating jump with the FM verses WFAN AM. Merlin with FM signals has not made a dent against WINS / WCBS or WBBM.
WEPN-FM got a short term bump with Knicks and Rangers playoff games. They might get a bump when the Jets' season starts. CBS' contracts with both NY baseball teams are up at the end of the current season and WEPN-FM is expected to make a run at the Yankees. Sooner or later, CBS will have to move WFAN to FM.
Merlin hasn't made a dent against established CBS news stations in NY and Chicago because they aren't offering anything of substance. WINS, WCBS and WBBM have been all-news for more than four decades. Whether it's AM or FM, it's all in the programming.